I just tried clicking that link in my i386 rawhide firefox, no prolem. So it
seems that this is not 64 bit related, as you have it with the i386 version, and
that some special condition is needed to trigger it. Can you think of anything
special with your system, plugins, non default gtk theme, anything?

If I login with a new user, firefox-2.0.0.5-3.fc8.i386 the 'download' window
works...
even moving my original ~/.mozilla/firefox aside does not help, so it must be
something else..
But as Hans suggests (mid-air collision :o) ) :
Changing my gtk-theme back to the default fixes the crash !
Thanx, for the suggestion, I know now where to look (although with a less
exiting desktop ;o) ) I hope this might also be some help for the Original Poster.